1. Field of the Invention
The present invention relates to an integrated circuit package.
2. Background Information
Integrated circuits are typically assembled into a package that is mounted to a printed circuit board. There are many types of integrated circuit packages including quad flat pack, pin grid array and plastic ball grid array (PBGA) packages. A PBGA package typically contains an integrated circuit which is mounted to a substrate. A plurality of solder balls are attached to a bottom surface of the substrate and reflowed to mount the package to a printed circuit board. The printed circuit board may be a motherboard of a computer system. The substrate may have routing traces and vias which connect the integrated circuit to the solder balls.
The integrated circuit of a PBGA package is enclosed by a protective plastic material. The outer plastic material is typically formed with an injection mold process. The integrated circuit generates heat which must be removed from the package. The plastic material has a relatively low coefficient of thermal conductivity which can create undesirable junction temperatures for the integrated circuit. A thermal element such as a heat slug may be integrated into the plastic housing to facilitate the removal of heat generated by the integrated circuit.
The heat slug is typically integrated into the package by placing the slug, integrated circuit and substrate into a plastic mold cavity. Plastic material is then injected into the mold cavity. The plastic cures and becomes attached to the substrate, integrated circuit and heat slug. It has been found that the plastic material may flow between the heat slug and the integrated circuit to create a layer of plastic between the two components. The plastic layer increases the thermal impedance between the integrated circuit and the heat slug. The increase in thermal impedance may raise the junction temperatures of the integrated circuit. It would be desirable to provide a package and a process that would eliminate the formation of plastic between the thermal element and the integrated circuit.